Android平台Dropbear SSH隧道出现段错误问题求助

Hey there, let's work through this segmentation fault issue you're hitting with your Dropbear setup. I've debugged similar tunnel problems on Android before, so here are actionable steps to identify and fix the root cause:

1. Verify Dropbear Version Compatibility #

Segmentation faults often pop up when there's a mismatch between the Dropbear version on your Android device and the SSH server on your Linux host.

• On your Android device, run: dropbear -V to check the installed Dropbear version.
• On your Linux host, run ssh -V (if using OpenSSH) or dropbear -V (if using Dropbear) to confirm the host-side version.
  If there's a significant version gap, try updating Dropbear on your Android device to match the host's SSH implementation as closely as possible.

2. Secure Your RSA Key Permissions #

Dropbear is strict about key file permissions—incorrect settings can lead to crashes. Make sure your RSA key on Android has read/write access only for the owner:

chmod 600 "$RSA_KEY"

Also, confirm the key is in a format Dropbear supports. If you generated it with OpenSSH, try re-generating it directly with Dropbear to rule out format issues:

dropbearkey -t rsa -f /sdcard/dropbear_rsa_key

Use this new key in your dbclient command instead.

3. Debug Without Silent Output #

Your current dbclient command redirects all output to /sdcard/out, which hides real-time errors that could explain the crash. Try running the command without redirection first, and add verbose logging to catch issues:

dbclient -v -i "$RSA_KEY" -f -N -R 0:localhost:22 "$HOST" -y

The -v flag will print detailed connection logs—look for any errors before the segmentation fault occurs.

4. Check Dropbear Startup Context #

Ensure you're starting dropbear only after dbclient has successfully established the tunnel. A race condition where dropbear starts before the tunnel is up could cause unexpected crashes. Also, add verbose logging to the dropbear command to see what's happening when it crashes:

dropbear -E -v -R

The -v flag here will log detailed startup and connection events to stderr.

5. Rule Out SELinux Restrictions #

Many Android devices run SELinux in Enforcing mode, which can block Dropbear's network operations and lead to crashes. Temporarily switch to Permissive mode to test this:

setenforce 0

If the tunnel works after this, you'll need to create a custom SELinux policy to allow Dropbear's operations permanently.

6. Check for Resource Constraints #

Segmentation faults can also happen if your Android device is low on memory or CPU. Close any unused background apps, then re-run your tunnel commands to see if the crash persists. You can check memory usage with:

free -h

7. Simplify Your Setup Step-by-Step #

Strip down your commands to the basics to isolate the issue:

1. First, run dbclient without the -f (background) flag and without output redirection to confirm the connection stays stable.
2. Once the dbclient connection is confirmed, start dropbear with minimal flags (dropbear -R).
3. Try connecting from your Linux host using the port from the dbclient output.
   This step-by-step approach will help you pinpoint exactly which part of the setup is causing the crash.

Let me know what you find from these steps—we can narrow it down further once you have more details!

内容的提问来源于stack exchange，提问作者HaykBeglaryan